Unraveling the nutritional and therapeutic properties of ‘Kavuni’ a traditional rice variety of Tamil Nadu R. Valarmathi, M. Raveendran, S. Robin & N. Senthil
Journal of Plant Biochemistry and Biotechnology ISSN 0971-7811 J. Plant Biochem. Biotechnol. DOI 10.1007/s13562-014-0274-6
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Author's personal copy J. Plant Biochem. Biotechnol. DOI 10.1007/s13562-014-0274-6
ORIGINAL ARTICLE
Unraveling the nutritional and therapeutic properties of ‘Kavuni’ a traditional rice variety of Tamil Nadu R. Valarmathi & M. Raveendran & S. Robin & N. Senthil
Received: 22 March 2013 / Accepted: 16 December 2013 # Society for Plant Biochemistry and Biotechnology 2014
Abstract ‘Kavuni’ a traditional brownish black rice variety is known for its anti-diabetic properties and is grown under limited areas of Tamil Nadu, India. The present study was aimed at profiling the nutritional and therapeutic values of Kavuni grains in comparison with three other popularly eaten white rice varieties of Tamil Nadu viz., CO 50, IR64 and White Ponni. Biochemical analysis revealed the significant differences in the nutritional composition of Kavuni grains when compared to other three white rice genotypes viz., 29–35 % reduced level of total soluble sugars, low fat content (8–35 %), 21–52 % increased dietary fibre and 7–24 % increased total protein content. Kavuni grains had significantly higher amount of iron (20– 30 %), calcium (33–45 %), copper (9.5–14.7 %), sodium (21–38 %), potassium (7–15 %) and magnesium (8.9–26 %). GC-MS analysis showed that phenolic acids and flavonoids were predominant in the Kavuni grains whereas sugars and fatty acids were predominant in the grains of a white rice variety CO 50. Further, Kavuni was found to possess significantly higher levels of different carotenoids (β-carotene—46.2 μg/ 100 g; lutein—221.6 μg/100 g), total phenolics (28.8 μg/ 100 g) and higher anti-oxidant activity. Methanol and ethyl acetate extracts of Kavuni grains were found to exhibit significantly higher level of inhibitory activity against α-amylase and α-glucosidase than the extracts of CO 50 (α-amylase IC50— 0.1, 1.0 μg/ml and α-glucosidase IC50 0.04, 0.05 μg/ml). Keywords Rice . Kavuni . Biochemical analysis . Anti-diabetic and therapeutic properties R. Valarmathi : M. Raveendran (*) : N. Senthil Centre for Plant Molecular Biology and Biotechnology, Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu, India e-mail:
[email protected] S. Robin Centre for Plant Breeding and Genetics, Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu, India
Abbreviations NIST National Institute of Standards and Technology, MD, USA DPPH 2,2 diphenyl-1 picrylhydrazyl BHA Butylated hydroxy anisole NBT Nitroblue tetrazolium PMS Phenazine methosulfate FTC Ferric thiocyanate
Introduction Rice is a major staple food for half of the world’s population, providing 50 to 80 % of daily calorie intake (Khush 2005). Carbohydrates, proteins, fatty acids and micronutrients (vitamins and trace minerals) are the major nutrient components in rice. Traditional rice genetic resources in India are reported to harbor vast amount of genetic diversity including medicinal properties and aroma (Das and Oudhia 2003). These traditional varieties are potent sources for various agronomic traits as well as sources of many bioactive non nutrient components (Crozier et al. 2009). Due to introduction of high yielding, semi-dwarf rice varieties during first green revolution, the traditional varieties with desirable traits were ignored and are now rare in cultivation (Rekha et al. 2011). Popularly eaten white rice contains very low level of essential micronutrients, leading to the development of micronutrient deficiency upon continuous consumption which warrants the situation of developing micro-nutrient and vitamin rich rice through genetic engineering (Ye et al. 2000). Consumption of increased quantity of polished rice grains (high GI food) has also been shown to contribute for higher insulin resistance and dyslipidemia (low-high density lipoprotein) among the Asian population. Traditional coloured rice varieties are known to be rich in dietary fibre, resistant starch, minerals, carotenoids, flavanoids
Author's personal copy J. Plant Biochem. Biotechnol.
and polyphenols and consumption of grains of these pigmented rice varieties help in improving human health (Hanhineva et al. 2010; Jae et al. 2010; Hudson et al. 2000; Rao et al. 2010). The bioactive phytochemicals and micronutrient components from these traditional rice varieties as dietary supplements are expected to play a major role in attenuating the incidence of non-communicable diseases viz., cardiovascular diseases, diabetes, cancer and stroke (Vichapong et al. 2010). With the majority of world’s population consuming rice as staple food, developing therapeutic rice varieties with enhanced nutritive value will have greater impact on preventing the above life style disorders. Preliminary studies conducted by our group have resulted in the identification of a traditional dark brownish black rice variety “Kavuni” which is known for its anti-diabetic properties. Kavuni is known as a long duration, poor tillering and photosensitive traditional rice variety and owing to these traits it is not being cultivated widely. Morphologically, dehusked grains of Kavuni is dark brown to black in colour and the polished grains are light brown (Fig. 1). No systematic scientific studies have been conducted to unravel the nutritional and therapeutic properties of Kavuni. The present study reports the nutritional and therapeutic values of “Kavuni” in comparison with three major high yielding white rice varieties of Tamil Nadu viz., IR 64, CO 50 and White Ponni.
Estimation of total soluble sugars and amylose content Grains of all four rice genotypes were ground using a pestle and mortar till we get a fine powder. Total soluble sugars in the powdered rice samples were estimated using phenol sulphuric acid method and starch content was estimated using anthrone method by using glucose as the standard (Sigma, USA). The flour was defatted using 85 % methanol for 18 h, dried to equilibrate moisture content (12–15 %) and then used for amylose estimation. Amylose from defatted rice flour was estimated as described by Sowbhagya and Bhattacharya (1979) using potato amylose (Sigma, USA) as a standard. Proximate analysis The total nitrogen content in the grains of all the four rice genotypes was estimated using the micro-Kjeldahl method (AOAC 2000) and the crude protein content was determined as Total N × 5.95 (AOAC 2000). Crude lipid content was determined gravimetrically after Soxhlet extraction with petroleum ether (60 grades) and subsequently evaporated to dryness on a steam bath (AOAC 1990). Dietary fibre and total ash contents were estimated using the method described by Englyst and Hudson (1996). Mineral analysis
Materials and methods Genetic material Four rice genotypes namely, a brownish black therapeutic rice variety “Kavuni” and three major high yielding white rice varieties of Tamil Nadu viz., IR 64, CO 50 and White Ponni were used in this study (Table 1). Nucleus seeds of all the four rice genotypes were obtained and raised during Kharif’ 2010 (June to December) at Department of Rice, Centre for Plant Breeding and Genetics, Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu, India. The well dried seeds with optimum moisture content (approx.13 %) were dehusked manually, powdered and stored at 4 °C until analysis.
Mineral composition (Fe, Zn, Ca, Mg, Na, K, Cu etc.,) in the grains of all four rice genotypes was determined using Atomic Absorption Spectrophotometry (Perkin-Elmer, Analysist A 700) after digestion with concentrated nitric acid (AOAC 2000). Scanning electron microscopy (SEM) The ultrastructure of macromolecule arrangement in the grains of Kavuni and a white rice genotype CO 50 was analyzed using a Scanning Electron Microscope (FEI Quanta 250, Icon analytical, FEI, USA). Dehusked grains of Kavuni and CO 50 were broken along the natural fracture planes and mounted on round aluminum stubs with the aid of double side adhesive
Fig. 1 Morphological features of panicle and grains of Kavuni (a panicle; b unpolished grain; c polished grains)
Author's personal copy J. Plant Biochem. Biotechnol. Table 1 Details on agronomic characters of the rice genotypes used in the present study Genotype
Origin
Days to maturity (days)
Pedigree
Agronomic features
Kavuni
Traditional variety, Tamil Nadu
135–140
Not known
CO 50
TNAU, Coimbatore, India
130–135
CO 43 × ADT 48
IR64
IRRI, Philippines
90–120
IR 5657 × IR 2061
Improved White Ponni
TNAU, Coimbatore, India
135–140
Taichung 65/2 × Mayang Ebos-80
Low yielding, poor tillering, long duration photosensitive, brownish black kernel High yielding, tolerant to BLB, photo insensitive and white kernel High yielding, fine quality, medium duration photo insensitive and white kernel High yielding, fine grain, good cooking quality, long duration, photo insensitive and white kernel
tape. The samples were scanned and selected regions were photographed. Metabolite extraction and GC/MS analysis Metabolite composition in the grains of Kavuni and a white rice variety CO 50 was studied by using GC/MS. Finely ground rice flour (30 mg) was extracted with methanol-water and then with chloroform (Fiehn et al. 2000). Ribitol (50 μl, 0.2 mg/ml in water) and nonadecanoic acid (50 μl, 2 mg/ml in chloroform) were added as internal standards and filtered using 0.22 μm PVDF syringe filter (Millipore, Ireland). The extracts were concentrated using a Speed Vac., and then derivatized by adding 80 μl of MSTFA. About 1 μl of the samples were injected into GC injection port (AI3000 II, Thermo Fischer Scientific, USA) connected to a GC/MS (TRACE™ GC Ultra with DSQII Quadrupole mass spectrometer and capillary column of 30 cm in length, 0.25 mm diameter and 0.25 μm film thickness-Agilent, DB-5 ms Ultra Inert, 122-5532). The injection port temperature was maintained at 250 °C, the oven temperature was programmed at 70 °C (5 min hold) and increased at the rate of 5 °C/min to 300 °C. Helium was used as a carrier gas at a flow rate of 1 ml/s. The electron ionization source temperature was maintained at 250 °C and the abundances of ions in the range of 50–600 m/z were scanned at a rate of 1.1 scans/s. Data obtained through GC/MS analysis was analyzed using X-Caliber software package. Table 2 Total soluble sugars and proximate contents in the grains of Kavuni and three white rice varieties of Tamil Nadu
Values are mean ± standard error of five determinations, values are significantly different at p
